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Translocation of 14C-haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} in quackgrass [Agropyron repens (L.) Beauv. # AGRRE] from the treated area (the middle 2.5 cm of the second of three leaves) to the lower leaves was reduced in plants in which 0.56 kg/ha of acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} or bentazon [3-1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one-2,2-dioxide] was added in tank mixture to a 0.07 kg ai/ha application of haloxyfop. Reduced translocation did not occur when haloxyfop rates were increased to 0.28 and 1.1 kg/ha. Bentazon reduced absorption of 14C-DPX-Y6202 {2-[4-[(6-chloro-2-quinoxalinyl)oxy] phenoxy] propionic acid} when applied in tank mixtures with 0.28 and 1.1 kg ai/ha DPX-Y6202. There was less 14C-DPX-Y6202 in the leaf tips of plants treated with 0.07 kg/ha DPX-Y6202 plus 0.56 kg/ha acifluorfen in tank mixture. Relatively small amounts of both 14C-haloxyfop and DPX-Y6202 accumulated in the rhizome and adjacent shoots and acifluorfen did not influence translocation to these plant parts. Considerably more 14C-haloxyfop than 14C-DPX-Y6202 was absorbed by quackgrass. Treatment of quackgrass with acifluorfen or bentazon 24 h prior to application of 14C-haloxyfop or 14C-DPX-Y6202 did not influence absorption or translocation.

Two strains of crownvetch (Coronilla varia L. # CZRVA) rhizobia were cultured in vitro with various rates of atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and bifenox [methyl 5-(2,4-dichlorophenoxy)-2-nitrobenzoate]. Growth, measured turbidimetrically over 48 h, was similar for both strains. Atrazine and bifenox significantly reduced bacterial growth after 14 and 36 h, respectively, only at the highest concentrations tested (463 μM atrazine and 292 μM bifenox). Since growth of crownvetch rhizobia was apparently not affected by rates of atrazine or bifenox above reasonable soil solution concentrations, it is likely that herbicidal effects on nodulation were due to toxicity to the host plant rather than toxicity to these bacteria. In a growth chamber experiment, total nodule activity (TNA) and carbon dioxide exchange rate (CER) were measured simultaneously in an effort to distinguish direct atrazine effects on nodule function from indirect effects due to inhibition of photosynthesis and a resulting decrease in photosynthate supply to nodules. When 5 and 50 mg atrazine per kg soil were applied to intact plants, CER was severely reduced within 24 h, but similar reductions in TNA were not observed until 48 h after treatment. Total nodule activity was reduced similarly by atrazine and defoliation; the application of atrazine to defoliated plants did not inhibit TNA more than did defoliation alone. The data indicate that reductions in crownvetch nodule activity by atrazine are due to inhibition of photosynthesis or other processes rather than direct toxicity to N fixation.

The cross-resistance of triazine-resistant biotypes of smooth pigweed (Amaranthus hybridus L. # AMACH), common lambsquarters (Chenopodium album L. # CHEAL), common groundsel (Senecio vulgaris L. # SENVU), and the crop canola (Brassica napus L. var. Atratower) to a selection of herbicides was evaluated at both the whole plant and chloroplast level. The triazine-resistant biotypes of all four species showed a similar pattern of cross-resistance, suggesting that a similar mutation had occurred in each species. The four triazine-resistant biotypes were resistant to injury from atrazine [6-chloro-N-ethyl-N′-(1-methylethyl)-1,3,5-triazine-2,4-diamine], bromacil [5-bromo-6-methyl-3-(1-methylpropyl)-2,4-(1H,3H)pyrimidinedione], and pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone] and were slightly resistant to buthidazole {3-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-4-hydroxy-1-methyl-2-imidazolidinone}. The triazine-resistant biotypes were more sensitive to dinoseb [2-(1-methylpropyl)-4,6-dinitrophenol]. Triazine-resistant smooth pigweed showed resistance to cyanazine {2-[[4-chloro-6-(ethylamino)-1,3,5-triazin-2-yl] amino]-2-methylpropanenitrile} and metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] with slight resistance to linuron [N′-(3,4-dichlorophenyl)-N-methoxy-N-methylurea] and desmedipham {ethyl [3-[[(phenylamino)carbony] oxy] phenyl] carbamate}. There was little or no resistance to diuron [N′-(3,4-dichlorophenyl)-N,N-dimethylurea], bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide], or dicamba (3,6-dichloro-2-methoxybenzoic acid). Parallel studies at the chloroplast level indicated that the degree of resistance to inhibition of photosynthetic electron transport was highly correlated with the degree of resistance to herbicidal injury. This correlation indicates that atrazine, cyanazine, metribuzin, pyrazon, bromacil, linuron, desmedipham, and buthidazole cause plant injury by inhibition of photosynthesis. This correlation also indicates that triazine resistance and cross-resistance at the whole plant level is due to decreased sensitivity at the level of photosynthetic electron transport. Cross-resistance to numerous additional herbicides was evaluated on isolated chloroplast thylakoid membranes and these results are discussed. 14C-atrazine was displaced from thylakoid membranes by several herbicides, indicating that these herbicides compete for a common binding site.

Sorghum [Sorghum bicolor (L.) Moench. ‘G-623 GBR’] bioassays indicated that shoot growth was more susceptible to metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] and more responsive to the antidote CGA-92194 {α-[(1,3-dioxolan-2-yl-methoxy)-imino] benzeneacetonitrile} than root growth. Seed treatment with CGA-92194 increased seedling shoot tolerance to metolachlor approximately tenfold. CGA-92194 seed treatment enhanced shoot absorption of 14C-metolachlor approximately twofold. Metolachlor was initially metabolized to the glutathione conjugate in untreated shoots and those treated with CGA-92194. However, CGA-92194 seed treatment caused accelerated metolachlor metabolism in the shoot, decreasing metolachlor content and increasing formation of the glutathione conjugate. Cyometrinil {(Z)-α[(cyanomethoxy)imino] benzeneacetonitrile}, flurazole [phenylmethyl 2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylate], naphthalic anhydride (1H,3H-naphtho[1,8-cd]-pyran-1,3-dione), and dichlormid (2,2-dichloro-N,N-di-2-propenylacetamide) also protected sorghum from metolachlor injury and enhanced metolachlor absorption and metabolism. The degree of protection conferred by a particular antidote was correlated with its ability to enhance metabolism of metolachlor in shoot tissue. These results are consistent with the hypothesis that the above antidotes protect sorghum from metolachlor injury by inducing rapid detoxification of metolachlor through conjugation with glutathione.

Pricklypear (Opuntia spp.) is a major constraint to rangeland livestock production in several resource areas of Texas. The phenological and physiological stages of pricklypear have heretofore been ignored in relation to timing of herbicide applications. The phenology, percent total nonstructural carbohydrates (TNC), and water content in Lindheimer pricklypear (Opuntia lindheimeri Engelm. # OPULI) were monitored biweekly for 2 yr in the southern Rolling Plains of Texas. TNC in cladophylls, crowns, and roots declined sharply from bud break (late March to late April) through the period of rapid development of new cladophylls and fruits, with minimum levels occurring during mid-July to early August. This depletion period coincides with the period when control has traditionally been attempted with broadcast applications of translocated herbicides with erratic results. Replenishment of TNC in cladophylls and basal crowns occurred during August through March or mid-April; major increases in root TNC occurred from early autumn through midwinter. Application of herbicide in late summer, autumn, or winter when TNC is being replenished in organs bearing meristematic tissue may be more effective for pricklypear control if the herbicide is translocated with photosynthates.

Translocation and metabolism of 14C-2,4-D [(2,4-dichlorophenoxy)acetic acid] and effects of 2,4-D on protein synthesis were compared in ‘T–68’ (2,4-D tolerant) and ‘Viking’ (susceptible) birdsfoot trefoil (Lotus corniculatus L.) in an attempt to elucidate some tolerance mechanisms. After 14C-2,4-D was applied to upper trifoliate leaves, significantly less 2,4-D was found in stems, in leaves below the treated leaves, and in roots of T–68 compared to Viking. More 2,4-D was bound to alcohol-insoluble cellular constituents of T–68 leaves, stems, and roots. When alcohol-soluble components were fractionated, slightly more 14C water-soluble compounds were found in T–68, indicating further inactivation by glycosylation. No amino acid-2,4-D conjugates were found. The rate of 14CO2 evolution from 14C-2,4-D treated seedlings in T–68 was five times that in Viking. Protein synthesis appeared to be more rapid in T–68 but the relationship to 2,4-D was not clear. In part, 2,4-D resistance in T–68 may result from its ability to inactivate 2,4-D by differential binding and conjugation and by side chain breakdown as indicated by 14CO2 release.

An isolate of Sclerotinia sclerotiorum (Lib.) de Bary collected from a Canada thistle [Cirsium arvense (L.) Scop. # CIRAR] plant in Montana proved pathogenic on Canada thistle in field trials. In addition to attacking the thistle crown and causing wilting and death of the shoots, S. sclerotiorum also infected the root system. The high percentage of thistle shoot kill (20 to 80%) after treatment, and subsequent reduction in plant thistle density the following year, demonstrated the potential of S. sclerotiorum as a biological control agent for Canada thistle in Montana.

The effects of johnsongrass [Sorghum halepense (L.) Pers. # SORHA] infestations were determined during a 2-yr study on sugarcane (Saccharum officinarum L. ‘CP-65-357’) yield. Both cane and sugar yields were lower (36 and 31%, respectively) in plots heavily infested with johnsongrass than in weed-free plots. Sugarcane yields were inversely influenced by johnsongrass equivalents (the sum of the values obtained by multiplying the number of clumps by their corresponding importance value for each plot). In 1983, both johnsongrass standing crop and johnsongrass equivalents correlated negatively with cane yield much better than any other factor combinations, while in 1984, the same was true for stalk population. Substantial yield reductions from johnsongrass interference were observed at johnsongrass infestation levels higher than 15 to 35%.

Two distinctive leaf forms have been described in the morningglory species Ipomoea hederacea (L.) Jacq. These are identified as ivyleaf morningglory [I. hederacea (L.) Jacq. # IPOHE] and entireleaf morningglory [I. hederacea (L.) Jacq. var. integriuscula Gray # IPOHG]. Controlled matings were made between pure breeding forms of plants with these two leaf types. The first generation progeny (F1) were all ivyleaf and the second generation (F2) was segregated in a 3:1 ratio (ivyleaf to entireleaf). The data fit a single gene model for determination of leaf shape, with ivyleaf being the dominant allele. Despite the dominance of the ivyleaf trait, the abundance of the entireleaf phenotype in the Mississippi Delta was higher than that of ivyleaf. Ipomoea hederacea is a facultative self-pollinator and other annual morningglory species found in the same area are also self-pollinated.

The beetle Oberea erythrocephala, whose larvae mine stems and roots of leafy spurge (Euphorbia esula L. # EPHES), was introduced into Oregon, Montana, and Wyoming between 1980 and 1984. Although it was not recovered in Oregon and Wyoming, it became established at two of three release sites in Montana and appears to be accepting leafy spurge plants at a fourth.

Chemicals that stimulate germination of curly dock seed (Rumex crispus L. # RUMCR) and urediniospores of curly dock rust [Uromyces rumicis Schum. (Wint.)], an obligate parasite of this weed, were studied and compared. Methyl salicylate, benzyl cyanide, and benzonitrile were the best stimulators of germination of curly dock seed. The compounds tested were most effective at concentrations ranging from 250 to 1000 μl/L. A 500 μl/L concentration of methyl salicylate caused 99% of the curly dock seed to germinate. Exposure to volatiles from 10 μl methyl salicylate or octyl cyanide for 16 to 24 h was required for maximum stimulation of curly dock seed germination in 10 days. Benzonitrile, methyl-2,4-dihydroxybenzoate, 3-cyanophenol, 2-heptanone, and benzaldehyde were the most effective of 45 compounds tested on urediniospores of curly dock rust. Benzonitrile was most active of 19 compounds tested on both seed and spores. Benzyl cyanide, 4-methoxybenzonitrile, benzaldehyde, and methyl 2,4-dihydroxybenzoate also were active on both propagules.

Broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash # BRAPP has recently become the dominant annual grass in certain fields of the North Carolina Coastal Plains. Previously, fall panicum (Panicum dichotomiflorum Michx. # PANDI) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA] were the dominant annual grasses in the region. One of the possible reasons for the observed population shift could be production of inhibitors or stimulators by one species that affects the population dynamics of the other species. Studies were initiated to evaluate the effects of broadleaf signalgrass, large crabgrass, and fall panicum residue, applied as a mulch or soil incorporated, on five indicator species: the three weeds themselves, corn (Zea mays L.), and soybean [Glycine max (L.) Merr.]. At expected residue levels, the degree of inhibition or stimulation from fall panicum and broadleaf signalgrass was determined to be significant for some indicator species. When such responses were seen, the amount of residue necessary to produce these results was usually within the concentrations normally observed in field situations. Based on these results, it appears that the observed population shift is partially mediated by the production of inhibitors or stimulators through plant residue. Other factors such as differential herbicide selectivity and crop rotation are being investigated.

The persistence of biologically active metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one] and its ethylthio analog [4-amino-6-(1,1-dimethylethyl)-3-(ethylthio)-1,2,4-triazin-5(4H)-one] were compared using an intact-plant chlorophyll fluorescence bioassay technique with oats (Avena sativa L.) and wheat (Triticum aestivum L.). Degradation of metribuzin phytotoxicity at concentrations of 0 to 1 ppm (w/w) ai in a Pond Creek silt loam soil was linear over time, with a half-life of 8 days at 35 C. Initial degradation of the biologically active ethylthio analog was much more rapid than for metribuzin, with a decrease in rate at later time intervals. A quadratic function best described this degradation pattern. The initial degradation rate of phytotoxicity for the ethylthio analog indicated a half-life of 4 days at 35 C. Soil pH had no significant influence on the activity or persistence of either herbicide within the range 4.9 to 6.9.

Preemergence applications of herbicides were evaluated for their effect on establishment of zoysiagrass (Zoysia japonica Steud.) with competition from either smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl. # DIGIS] or goosegrass [Eleusine indica (L.) Gaertn. # ELEIN]. When ‘Meyer’ and ‘Belair’ zoysiagrass plugs were grown in sand and treated in the greenhouse, none of the herbicides reduced root weight or length. When plugs were grown in a Sassafrass sandy loam, bensulide {O,O-bis(1-methylethyl)-S-[2-[(phenylsulfonyl)amino] ethyl] phosphorodithioate} and simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine) reduced root weight, and simazine reduced root length of Belair, but not Meyer. In smooth crabgrass-infested field plots, more stolons were produced from Meyer plugs treated with simazine, oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one}, and siduron [N-(2-methylcyclohexyl)-N′-phenylurea] than plugs treated with bensulide, metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], or the untreated control. At the end of two growing seasons, metribuzin-treated plots had significantly less zoysiagrass than other plots. Oxadiazon, DCPA (dimethyl tetrachloroterephthalate), and siduron enhanced the field establishment rate where Meyer zoysiagrass was competing with high populations of smooth crabgrass.

In order to find the most effective and economical method of incorporation, six preplant herbicides for cotton (Gossypium hirsutum L.) were incorporated with a tandem disk or field cultivator, or sprayed on unbedded soil prior to bedding with a disk bedder. These treatments were compared to incorporating sprayed beds with a rolling cultivator and no incorporation. A mixed population of pigweed (Amaranthus hybridus L. # AMACH and Amaranthus retroflexus L. # AMARE) was present each year. There was no significant difference in pigweed control among incorporation with a disk, field cultivator, or rolling cultivator. Puncturevine (Tribulus terrestris # TRBTE) and barnyardgrass [Echinochloa crus-galli (L.) Beauv. # ECHCG] were controlled best following rolling cultivator incorporation. Cotton lint yields were not affected by incorporation methods or herbicides. Economic analysis and weed control indicate that the field cultivator was the best way of incorporation.

Spring-applied herbicides were evaluated in the field in 1982 through 1984 in western Nebraska for selective weed control in irrigated seedling alfalfa (Medicago sativa L. ‘Appollo’). Weed densities were least in plots treated preplant with benefin [N-butyl-N-ethyl-2,6-dinitro-4-(trifluoromethyl)benzenamine] in combination with postemergence applications of 2,4-DB [4-(2,4-dichlorophenoxy) butyric acid]. Combinations of sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one} with bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and fluazifop-butyl {(±)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} with bromoxynil provided less grass control than sethoxydim or fluazifop-butyl applied alone. Annual weeds did not reduce alfalfa stand density.

Ten herbicides were evaluated for broomrape (Orobanche ramosa L. # ORARA) control and their effect on growth, yield, and chemical composition of four tobacco (Nicotiana tabaccum L.) cultivars. Of the preplant-incorporated (PPI) herbicides, only pebulate (S-propyl butylethylcarbamothioate) at 7.2 kg ai/ha and metham (methylcarbamodithioic acid) at 66 kg ai/ha provided, although inconsistently, 30 to 50% broomrape control in oriental but not in burley tobacco. Single postemergence (POE) applications of glyphosate [N-(phosphonomethyl)glycine] at 0.2 kg ai/ha or MH (1,2-dihydro-3,6-pyridazinedione) at 0.7 kg ai/ha at 40 days after transplanting resulted in 60 to 80% broomrape control. Glyphosate or MH applications at 40 days after transplanting and again at 60 days resulted in 100% and 80 to 90% control, respectively. Very good (80 to 90%) control also occurred with pebulate (PPI) at 7.2 kg ai/ha followed by glyphosate (POE) at 0.2 kg ai/ha at 40 days after transplanting. Tobacco yield increased significantly, compared to that of untreated plots, where glyphosate or MH was used, but nicotine, total nitrogen, and reducing sugar contents were not significantly affected.

Kentucky bluegrass (Poa pratensis L. ‘Parade’, ‘Adelphi’, ‘Glade’, and ‘Rugby’ # POAPR) and tall fescue (Festuca arundinacea Schreb. ‘Kentucky 31’ # FESAR) were treated in field experiments with chlorsulfuron {2-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino] carbonyl] benzenesulfonamide}. The objectives of the two experiments were to determine if this herbicide has the potential to be used for selective control of tall fescue in Kentucky bluegrass turf. Chlorsulfuron treatments included single rates of 0, 18, 35, 71, 141, 212, and 282 g ai/ha and split rates, applied 14 days apart, of 18 + 18, 35 + 35, 71 + 71, 141 + 141, and 212 + 212 g/ha. Clipping weights and turfgrass quality ratings were taken in both experiments. Kentucky bluegrass showed a higher tolerance to the chemical, with no decrease in turf quality at the highest single and split application rates in both experiments. However, as the chlorsulfuron rate increased, clipping weight decreased. Tall fescue showed a low tolerance to the chemical and was controlled at single rates of 141 g/ha and split rates of 141 + 141 g/ha and greater. Although the tall fescue recovered from damage at single rates of 71 g/ha and split rates of 71 + 71 g/ha, severe growth inhibition and discoloration of aboveground tissue occurred at the lower rates. Twelve months after the first chlorsulfuron was applied in each experiment, glyphosate [isopropylamine salt of N-(phosphonomethyl)glycine] was sprayed over the plots to kill all existing plant material, and Kentucky bluegrass was seeded into the plots 2 weeks later at the rate of 0.75 kg/100 m2. There was no inhibition of bluegrass seed germination at any of the rates of chlorsulfuron.